The four factors of 91 are 1, 7, 13 and 91. The factor pairs of 91 are 1 x 91 and 7 x 13. The prime factors of 91 are 7 and 13. The prime factorization of 91 is 7 x 13 …Finding the prime factors: The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19. 91 cannot evenly be divided by 2, 3, or 5. Dividing 91 by 7 gives 13, which is also prime. This means that the prime factors of 91 are 7 and 13.